1. Field of the Invention
This invention relates to manifolds for pumps used in handling cryogenic liquids, and more particularly, to a cryogenic pump manifold that utilizes a subcooler and heat exchanger to cool liquid entering the pump.
2. Description of the Prior Art
Cryogenic liquids are those which must be greatly refrigerated to keep them in a liquid state under reasonable pressures. Liquid nitrogen is one example. Various equipment has been developed for the handling and storage of such liquids, including pumps for transferring the liquid from one location to another, such as from a storage container to another area in which the liquid will be utilized. One type of pump which has been used for this purpose is a reciprocating piston or plunger pump, such as the Halliburton Triplex pump. Typically, an inlet or suction manifold is mounted on the pump connecting the pump suction to a source of the cryogenic liquid. It is desirable to provide the coldest possible cryogenic liquid to the pump inlet because this is necessary to meet the most efficient net positive suction head (NPSH) requirements of the pump. In all cryogenic pumps, the lower the suction fluid temperature the better will be the overall performance of the pump.
Insulating the suction manifold and inlet piping for the pump keeps the incoming liquid cool. This has the limitation of the capabilities of the insulation depending upon ambient conditions, and, of course, provides no additional cooling. One device which has been developed and which has had success in providing some cooling is a cryogenic subcooler on the pump inlet. A cryogenic subcooler is a device that takes the pressurized cryogenic liquid and uses a portion of it to produce a low temperature within the subcooler. This subcooler temperature is lower than the inlet liquid temperature because the portion of the inlet liquid that is released from the liquid flow to the subcooler is passed through an expansion device. This expansion usually causes the liquid to evaporate or "flash." The expansion and evaporation of the liquid into a gaseous state causes the temperature to drop and lowers the subcooler temperature. The lower temperature expanded gas reduces the temperature of the pressurized inlet liquid entering the pump, producing a refrigerated or "conditioned" liquid.
Previous subcoolers may not be able to create enough heat transfer in some cases, so that the liquid entering the pump is not adequately cooled to meet the pump NPSH requirements to obtain optimum pump performance. Therefore, there is a need for greater subcooling.
The present invention solves these problems by incorporating a heat exchanger in conjunction with the subcooler to increase heat transfer and provide more cooling of the liquid entering the pump through the suction manifold.
Another problem with inadequate subcooling is that prolonged ambient heat gain may mean that the pump cannot function for a long period of time. Therefore, there is also a need for more cooling to overcome this problem. The present invention addresses this in that the greater exchange of heat in the apparatus results in an elimination of, or at least reduction in, ambient heat gain that provides longer running periods for the pump.
An alternate embodiment of the present invention increases the cooling even more by increasing the evaporation of liquid through the subcooler and heat exchanger through use of a fluid ejector or jetting device.